As Apple prepares the release of three iPhones, the rumour mill is beginning to turn as more punters weigh up the benefits of owning an iPhone or a Samsung Galaxy.

Ten years after Steve Jobs unveiled the original iPhone in San Francisco, Apple is planning its most extensive iPhone line-up to date.

The upcoming launch is expected to include upgraded versions of the current two iPhone models – the iPhone 7 and 7 Plus – along with a new top-of-the-line handset with an overhauled look, according to people familiar with the matter.

The most talked about feature is the screen, which is thought to wrap across the face of the device, similar to Samsung's Edge series. Such a fundamental adjustment gives rise to a number of design considerations, such as the placement of the home button, volume controls and fingerprint scanner.

Melbourne tech positor Sonny Dickson drew attention during the week with a tweet titled "iPhone 8 looks to be taking a new direction" that features what appears to be a technical drawing of an iPhone design.

The illustration features what appears to be a space at the back below the Apple logo for a potential fingerprint scanner.

Samsung, Apple's biggest rival, solved the vanishing home button dilemma on the recent S8 and S8+ releases by placing its fingerprint scanner at the back, drawing criticism about its accessibility.

Those anxiously awaiting the redesigned iPhone, however, may have to wait because supply constraints could mean the device isn't readily available until one or two months after the typical winter introduction.

This year's new iPhone line-up comes at a critical time. Last year, Apple broke its typical upgrade cycle by retaining the same "iPhone shape" for a third consecutive year.

Samsung's new S8 line-up has thus far been well received despite last year's Note7 battery debacle.

Pre-orders for Samsung's Galaxy S8 smartphone exceeded those of its predecessor (S7), according to Samsung mobile chief Koh Dong-jin.

"It's still a bit early, but initial response to the pre-orders that have begun at various places across the world have been better than expected," he said.

The S8 will be the safest Galaxy smartphone to date due to measures implemented to avoid the battery failures, he said.

Despite rave reviews, a report in the Wall Street Journal has revealed the Samsung's S8's centrepiece also appears to be its Achilles heel: Bixby, its voice assistant (similar to Apple's Siri).

The report claims that some of Bixby's features work but it isn't able to respond to any user voice commands in English.

Apple's iPhone feature and design plans are still in flux and can change, said sources obtained by Bloomberg who are familiar with the matter. The sources asked not to be identified discussing Apple's private testing and design plans.

For its redesigned phone, Apple has tested multiple prototypes with manufacturing partners in Asia, including some versions that use curved glass and stainless steel, according to one of the sources.

One of the latest prototype designs includes symmetrical, slightly curved glass on the front and the back. The curves are similar in shape to those on the front of the iPhone 7. The new OLED screen itself is flat, while the cover glass curves into a steel frame.

Apple also tested a more ambitious prototype with the same slightly curved front and steel frame, but a glass back with more dramatic curves on the top and bottom like the original iPhone design from 2007, one of the sources said.

Apple is testing a screen that covers almost the entire front of the device, according to sources, resulting in a display slightly larger than that of the iPhone 7 Plus but an overall size closer to the iPhone 7.

Apple is purportedly also aiming to reduce the overall size of the handset by integrating the home button into the screen itself via software in a similar manner to Samsung's S8.

The overhauled iPhone will use an organic light-emitting diode display that more accurately shows colours, while the other two phones will continue to use liquid crystal display technology and come in the same 4.7-inch and 5.5-inch screen sizes as last year's iPhone 7 and iPhone 7 Plus.

Because of its early lead in the mobile OLED display space, Samsung will enjoy a rare upper hand in this year's high-end smartphone contest. At launch, Apple will exclusively use Samsung Display OLED panels for the redesigned iPhone, Bloomberg reported last year.

Apple suppliers have so far struggled to reliably produce heavily curved glass in mass quantities, so the company is more likely to ship the version with more subdued curves, one Bloomberg source added recently. Another source by Bloomberg claims Apple has ordered around 100 million of the glass panels from Samsung.

Spokespeople for Apple and Samsung declined to comment.

Apple has also experimented with integrating the iPhone's fingerprint scanner into the screen of the OLED version, which would be technically challenging, the sources said. It's currently unclear if that feature will make it into the final product.

Significant camera changes are also in testing for Apple's overhauled iPhone. For the back of the phone, Apple is testing versions of the phone with the dual-camera system positioned vertically, instead of horizontally like on the iPhone 7 Plus, which could result in improved photos.

Some prototypes in testing continue to include the slight camera bump found on current iPhones, rather than having them flush with the back surface, sources said.

Apple has explored adding augmented reality-based features and depth-of-field enhancements to its iPhone camera system, Bloomberg News reported. Company engineers in the past have also experimented with integrating cameras into screens, another person said.

Apple has been testing using faster processors, a person familiar with Apple's chip plans said. That's down from 16 nanometres for existing iPhones. The smaller processors are more efficient, allowing Apple to retain its battery life standards while adding more advanced features.

With wires